Caveolin-1 is required for contractile phenotype expression by airway smooth muscle cells

Mechanosensory entities and functionality of endothelial cells

The endothelial cells of the blood circulation are exposed to hemodynamic forces, such as cyclic strain, hydrostatic forces, and shear stress caused by the blood fluid's frictional force. Endothelial cells perceive mechanical forces via mechanosensors and thus elicit physiological reactions such as alterations in vessel width. The mechanosensors considered comprise ion channels, structures linked to the plasma membrane, cytoskeletal spectrin scaffold, mechanoreceptors, and junctional proteins. This review focuses on endothelial mechanosensors and how they alter the vascular functions of endothelial cells. The current state of knowledge on the dysregulation of endothelial mechanosensitivity in disease is briefly presented. The interplay in mechanical perception between endothelial cells and vascular smooth muscle cells is briefly outlined. Finally, future research avenues are highlighted, which are necessary to overcome existing limitations.

Zedoarondiol inhibits human bronchial smooth muscle cell proliferation through the CAV-1/PDGF signalling pathway

Airway remodelling in lung diseases can be treated by inhibiting excessive smooth muscle cell proliferation. Zedoarondiol (Zed) is a natural compound isolated from the Chinese herb Curcuma longa. The caveolin-1 (CAV-1) is widely expressed in lung cells and plays a key role in platelet-derived growth factor (PDGF) signalling and cell proliferation. This study aims to investigate the effect of Zed on human bronchial smooth muscle cell (HBSMC) proliferation and explore its potential molecular mechanisms. We assessed the effect of Zed on the proliferation of PDGF-stimulated HBSMCs and performed proteomic analysis to identify potential molecular targets and pathways. CAV1 siRNA was used to validate our findings in vitro. In PDGF-stimulated HBSMCs, Zed significantly inhibited excessive proliferation of HBSMCs. Proteomic analysis of zedoarondiol-treated HBSMCs revealed significant enrichment of differentially expressed proteins in cell proliferation-related pathways and biological processes. Zed inhibition of HBSMC proliferation was associated with upregulation of CAV1, regulation of the CAV-1/PDGF pathway and inhibition of MAPK and PI3K/AKT signalling pathway activation. Treatment of HBSMCs with CAV1 siRNA partly reversed the inhibitory effect of Zed on HBSMC proliferation. Thus, this study reveals that zedoarondiol potently inhibits HBSMC proliferation by upregulating CAV-1 expression, highlighting its potential value in airway remodelling and related diseases.

Prorelaxant E-type Prostanoid Receptors Functionally Partition to Different Procontractile Receptors in Airway Smooth Muscle

Prostaglandin E2 imparts diverse physiological effects on multiple airway cells through its actions on four distinct E-type prostanoid (EP) receptor subtypes (EP1-EP4). Gs-coupled EP2 and EP4 receptors are expressed on airway smooth muscle (ASM), yet their capacity to regulate the ASM contractile state remains subject to debate. We used EP2 and EP4 subtype-specific agonists (ONO-259 and ONO-329, respectively) in cell- and tissue-based models of human ASM contraction-magnetic twisting cytometry (MTC), and precision-cut lung slices (PCLSs), respectively-to study the EP2 and EP4 regulation of ASM contraction and signaling under conditions of histamine or methacholine (MCh) stimulation. ONO-329 was superior (<0.05) to ONO-259 in relaxing MCh-contracted PCLSs (log half maximal effective concentration [logEC50]: 4.9 × 10-7 vs. 2.2 × 10-6; maximal bronchodilation ± SE, 35 ± 2% vs. 15 ± 2%). However, ONO-259 and ONO-329 were similarly efficacious in relaxing histamine-contracted PCLSs. Similar differential effects were observed in MTC studies. Signaling analyses revealed only modest differences in ONO-329- and ONO-259-induced phosphorylation of the protein kinase A substrates VASP and HSP20, with concomitant stimulation with MCh or histamine. Conversely, ONO-259 failed to inhibit MCh-induced phosphorylation of the regulatory myosin light chain (pMLC20) and the F-actin/G-actin ratio (F/G-actin ratio) while effectively inhibiting their induction by histamine. ONO-329 was effective in reversing induced pMLC20 and the F/G-actin ratio with both MCh and histamine. Thus, the contractile-agonist-dependent differential effects are not explained by changes in the global levels of phosphorylated protein kinase A substrates but are reflected in the regulation of pMLC20 (cross-bridge cycling) and F/G-actin ratio (actin cytoskeleton integrity, force transmission), implicating a role for compartmentalized signaling involving muscarinic, histamine, and EP receptor subtypes.

A Role of Caveolae in Trabecular Meshwork Mechanosensing and Contractile Tone

Polymorphisms in the CAV1/2 gene loci impart increased risk for primary open-angle glaucoma (POAG). CAV1 encodes caveolin-1 (Cav1), which is required for biosynthesis of plasma membrane invaginations called caveolae. Cav1 knockout mice exhibit elevated intraocular pressure (IOP) and decreased outflow facility, but the mechanistic role of Cav1 in IOP homeostasis is unknown. We hypothesized that caveolae sequester/inhibit RhoA, to regulate trabecular meshwork (TM) mechanosensing and contractile tone. Using phosphorylated myosin light chain (pMLC) as a surrogate indicator for Rho/ROCK activity and contractile tone, we found that pMLC was elevated in Cav1-deficient TM cells compared to control (131 ± 10%, n = 10, p = 0.016). Elevation of pMLC levels following Cav1 knockdown occurred in cells on a soft surface (137 ± 7%, n = 24, p < 0.0001), but not on a hard surface (122 ± 17%, n = 12, p = 0.22). In Cav1-deficient TM cells where pMLC was elevated, Rho activity was also increased (123 ± 7%, n = 6, p = 0.017), suggesting activation of the Rho/ROCK pathway. Cyclic stretch reduced pMLC/MLC levels in TM cells (69 ± 7% n = 9, p = 0.002) and in Cav1-deficient TM cells, although not significantly (77 ± 11% n = 10, p = 0.059). Treatment with the Cav1 scaffolding domain mimetic, cavtratin (1 μM) caused a reduction in pMLC (70 ± 5% n = 7, p = 0.001), as did treatment with the scaffolding domain mutant cavnoxin (1 μM) (82 ± 7% n = 7, p = 0.04). Data suggest that caveolae differentially regulate RhoA signaling, and that caveolae participate in TM mechanotransduction. Cav1 regulation of these key TM functions provide evidence for underlying mechanisms linking polymorphisms in the Cav1/2 gene loci with increased POAG risk.

A narrative review of research advances in the study of molecular markers of airway smooth muscle cells

Background and Objective

Airway smooth muscle cells (ASMCs) are an important component of the airway. Their thickening and proliferation are important in pathological situations, such as airway remodeling in asthma, but their origin remains unclear. Therefore, characterizing molecular markers of ASMCs were sought to identify the source of increased ASMCs in asthmatic airway remodeling.

Methods

Articles for this review were derived from a review of the literature related to surface markers and biological properties of ASMCs and smooth muscle cells (SMCs) using PubMed, Google Scholar, and Web of Science.

Key Content and Findings

This review discusses several SMC molecular markers, describes the different developmental stages of SMCs that express different molecular markers, and summarizes several classical SMC molecular markers. However, the establishment of a specific molecular marker detection system for ASMCs still faces great challenges.

Conclusions

Although there is no recognized molecular marker detection system for ASMCs, and the study of the properties and sources of increased ASMCs in asthma airway remodeling is still in a state of exploration, the future is promising. Among the SMC markers described in this review, Myosin heavy chain 11 (MYH11) is a molecular marker for mature SMCs and Transgelin (TAGLN) is an early marker for SMC differentiation, and different molecular markers or combinations of molecular markers can be selected for the identification of the properties and sources of increased ASMCs in asthma airway remodeling according to the differentiation period and research needs.

Signaling Pathways Involved in the Development of Bronchopulmonary Dysplasia and Pulmonary Hypertension

The alveolar and vascular developmental arrest in the premature infants poses a major problem in the management of these infants. Although, with the current management, the survival rate has improved in these infants, but bronchopulmonary dysplasia (BPD) is a serious complication associated with a high mortality rate. During the neonatal developmental period, these infants are vulnerable to stress. Hypoxia, hyperoxia, and ventilation injury lead to oxidative and inflammatory stress, which induce further damage in the lung alveoli and vasculature. Development of pulmonary hypertension (PH) in infants with BPD worsens the prognosis. Despite considerable progress in the management of premature infants, therapy to prevent BPD is not yet available. Animal experiments have shown deregulation of multiple signaling factors such as transforming growth factorβ (TGFβ), connective tissue growth factor (CTGF), fibroblast growth factor 10 (FGF10), vascular endothelial growth factor (VEGF), caveolin-1, wingless & Int-1 (WNT)/β-catenin, and elastin in the pathogenesis of BPD. This article reviews the signaling pathways entailed in the pathogenesis of BPD associated with PH and the possible management.

Loss of Caveolin-1 and caveolae leads to increased cardiac cell stiffness and functional decline of the adult zebrafish heart

Caveolin-1 is the main structural protein of caveolae, small membrane invaginations involved in signal transduction and mechanoprotection. Here, we generated cav1-KO zebrafish lacking Cav1 and caveolae, and investigated the impact of this loss on adult heart function and response to cryoinjury. We found that cardiac function was impaired in adult cav1-KO fish, which showed a significantly decreased ejection fraction and heart rate. Using atomic force microscopy, we detected an increase in the stiffness of epicardial cells and cells of the cortical zone lacking Cav1/caveolae. This loss of cardiac elasticity might explain the decreased cardiac contraction and function. Surprisingly, cav1-KO mutants were able to regenerate their heart after a cryoinjury but showed a transient decrease in cardiomyocyte proliferation.

Caveolin-1 scaffolding domain peptide prevents hyperoxia-induced airway remodeling in a neonatal mouse model

Reactive airway diseases are significant sources of pulmonary morbidity in neonatal and pediatric patients. Supplemental oxygen exposure in premature infants contributes to airway diseases such as asthma and promotes development of airway remodeling, characterized by increased airway smooth muscle (ASM) mass and extracellular matrix (ECM) deposition. Decreased plasma membrane caveolin-1 (CAV1) expression has been implicated in airway disease and may contribute to airway remodeling and hyperreactivity. Here, we investigated the impact of clinically relevant moderate hyperoxia (50% O₂) on airway remodeling and caveolar protein expression in a neonatal mouse model. Within 12 h of birth, litters of B6129SF2J mice were randomized to room air (RA) or 50% hyperoxia exposure for 7 days with or without caveolin-1 scaffolding domain peptide (CSD; caveolin-1 mimic; 10 µl, 0.25 mM daily via intraperitoneal injection) followed by 14 days of recovery in normoxia. Moderate hyperoxia significantly increased airway reactivity and decreased pulmonary compliance at 3 wk. Histologic assessment demonstrated airway wall thickening and increased ASM mass following hyperoxia. RNA from isolated ASM demonstrated significant decreases in CAV1 and cavin-1 in hyperoxia-exposed animals while cavin-3 was increased. Supplementation with intraperitoneal CSD mitigated both the physiologic and histologic changes observed with hyperoxia. Overall, these data show that moderate hyperoxia is detrimental to developing airway and may predispose to airway reactivity and remodeling. Loss of CAV1 is one mechanism through which hyperoxia produces these deleterious effects. Supplementation of CAV1 using CSD or similar analogs may represent a new therapeutic avenue for blunting hyperoxia-induced pulmonary damage in neonates.

NF-κB and GATA-Binding Factor 6 Repress Transcription of Caveolins in Bladder Smooth Muscle Hypertrophy

Caveolins (CAVs) are structural proteins of caveolae that function as signaling platforms to regulate smooth muscle contraction. Loss of CAV protein expression is associated with impaired contraction in obstruction-induced bladder smooth muscle (BSM) hypertrophy. In this study, microarray analysis of bladder RNA revealed down-regulation of CAV1, CAV2, and CAV3 gene transcription in BSM from models of obstructive bladder disease in mice and humans. We identified and characterized regulatory regions responsible for CAV1, CAV2, and CAV3 gene expression in mice with obstruction-induced BSM hypertrophy, and in men with benign prostatic hyperplasia. DNA affinity chromatography and chromatin immunoprecipitation assays revealed a greater increase in binding of GATA-binding factor 6 (GATA-6) and NF-κB to their cognate binding motifs on CAV1, CAV2, and CAV3 promoters in obstructed BSM relative to that observed in control BSM. Knockout of NF-κB subunits, shRNA-mediated knockdown of GATA-6, or pharmacologic inhibition of GATA-6 and NF-κB in BSM increased CAV1, CAV2, and CAV3 transcription and promoter activity. Conversely, overexpression of GATA-6 decreased CAV2 and CAV3 transcription and promoter activity. Collectively, these data provide new insight into the mechanisms by which CAV gene expression is repressed in hypertrophied BSM in obstructive bladder disease.

Gene expression profiles and signaling mechanisms in α2B-adrenoceptor-evoked proliferation of vascular smooth muscle cells

BACKGROUND

α2-adrenoceptors are important regulators of vascular tone and blood pressure. Regulation of cell proliferation is a less well investigated consequence of α2-adrenoceptor activation. We have previously shown that α2B-adrenoceptor activation stimulates proliferation of vascular smooth muscle cells (VSMCs). This may be important for blood vessel development and plasticity and for the pathology and therapeutics of cardiovascular disorders. The underlying cellular mechanisms have remained mostly unknown. This study explored pathways of regulation of gene expression and intracellular signaling related to α2B-adrenoceptor-evoked VSMC proliferation.

RESULTS

The cellular mechanisms and signaling pathways of α2B-adrenoceptor-evoked proliferation of VSMCs are complex and include redundancy. Functional enrichment analysis and pathway analysis identified differentially expressed genes associated with α2B-adrenoceptor-regulated VSMC proliferation. They included the upregulated genes Egr1, F3, Ptgs2 and Serpine1 and the downregulated genes Cx3cl1, Cav1, Rhoa, Nppb and Prrx1. The most highly upregulated gene, Lypd8, represents a novel finding in the VSMC context. Inhibitor library screening and kinase activity profiling were applied to identify kinases in the involved signaling pathways. Putative upstream kinases identified by two different screens included PKC, Raf-1, Src, the MAP kinases p38 and JNK and the receptor tyrosine kinases EGFR and HGF/HGFR. As a novel finding, the Src family kinase Lyn was also identified as a putative upstream kinase.

CONCLUSIONS

α2B-adrenoceptors may mediate their pro-proliferative effects in VSMCs by promoting the activity of bFGF and PDGF and the growth factor receptors EGFR, HGFR and VEGFR-1/2. The Src family kinase Lyn was also identified as a putative upstream kinase. Lyn is known to be expressed in VSMCs and has been identified as an important regulator of GPCR trafficking and GPCR effects on cell proliferation. Identified Ser/Thr kinases included several PKC isoforms and the β-adrenoceptor kinases 1 and 2. Cross-talk between the signaling mechanisms involved in α2B-adrenoceptor-evoked VSMC proliferation thus appears to involve PKC activation, subsequent changes in gene expression, transactivation of EGFR, and modulation of kinase activities and growth factor-mediated signaling. While many of the identified individual signals were relatively small in terms of effect size, many of them were validated by combining pathway analysis and our integrated screening approach.

Caveolin-1: Functional Insights into Its Role in Muscarine- and Serotonin-Induced Smooth Muscle Constriction in Murine Airways

An increased bronchoconstrictor response is a hallmark in the progression of obstructive airway diseases. Acetylcholine and 5-hydroxytryptamine (5-HT, serotonin) are the major bronchoconstrictors. There is evidence that both cholinergic and serotonergic signaling in airway smooth muscle (ASM) involve caveolae. We hypothesized that caveolin-1 (cav-1), a structural protein of caveolae, plays an important regulatory role in ASM contraction. We analyzed airway contraction in different tracheal segments and extra- and intrapulmonary bronchi in cav-1 deficient (cav-1−/−) and wild-type mice using organ bath recordings and videomorphometry of methyl-beta-cyclodextrin (MCD) treated and non-treated precision-cut lung slices (PCLS). The presence of caveolae was investigated by electron microscopy. Receptor subtypes driving 5-HT-responses were studied by RT-PCR and videomorphometry after pharmacological inhibition with ketanserin. Cav-1 was present in tracheal epithelium and ASM. Muscarine induced a dose dependent contraction in all airway segments. A significantly higher Emax was observed in the caudal trachea. Although, caveolae abundancy was largely reduced in cav-1−/− mice, muscarine-induced airway contraction was maintained, albeit at diminished potency in the middle trachea, in the caudal trachea and in the bronchus without changes in the maximum efficacy. MCD-treatment of PLCS from cav-1−/− mice reduced cholinergic constriction by about 50%, indicating that cholesterol-rich plasma domains account for a substantial portion of the muscarine-induced bronchoconstriction. Notably, cav-1-deficiency fully abrogated 5-HT-induced contraction of extrapulmonary airways. In contrast, 5-HT-induced bronchoconstriction was fully maintained in cav-1-deficient intrapulmonary bronchi, but desensitization upon repetitive stimulation was enhanced. RT-PCR analysis revealed 5-HT1B, 5-HT2A, 5-HT6, and 5-HT7 receptors as the most prevalent subtypes in the airways. The 5-HT-induced-constriction in PCLS could be antagonized by ketanserin, a 5-HT2A receptor inhibitor. In conclusion, the role of cav-1, caveolae, and cholesterol-rich plasma domains in regulation of airway tone are highly agonist-specific and dependent on airway level. Cav-1 is indispensable for serotonergic contraction of extrapulmonary airways and modulates cholinergic constriction of the trachea and main bronchus. Thus, cav-1/caveolae shall be considered in settings such as bronchial hyperreactivity in common airway diseases and might provide an opportunity for modulation of the constrictor response.

γ-Tocotrienol Inhibits TGF-β1-Induced Contractile Phenotype Expression of Human Airway Smooth Muscle Cells

BACKGROUND

Tocotrienols, members of the vitamin E family, exist in four different isoforms (α, β, γ and δ tocotrienol) that have can be protective against brain damage, as well as having anticancer effects in vivo and in vitro. We have shown that γ-tocotrienol inhibits human airway smooth muscle cell proliferation and migration induced by platelet-derived growth factor (PDGF)-BB by suppressing RhoA activation. In this study, we tested whether γ-tocotrienol modulates transforming growth factor (TGF) -β-induced induction of human airway smooth muscle (ASM) into a contractile phenotype and concomitant synthesis of extracellular matrix proteins.

METHODS

ASM cells were stimulated with TGF-β1 (2 ng/mL) for 48 hours and the effect of γ-tocotrienol (50 μM) on α-smooth muscle actin, fibronectin and collagen I expression was assessed using Western blotting. The signaling pathways involved in TGF-β1 stimulation were also investigated.

RESULTS

TGF-β1 increased α-smooth muscle actin, fibronectin and collagen Ⅰ abundance by 3- to 5-fold. This response was inhibited significantly by γ-tocotrienol. Furthermore, γ-tocotrienol suppressed RhoA activation, but did not affect Smad2 or Smad3 phosphorylation.

CONCLUSION

These results indicate that γ-tocotrienol has potential for benefit in modulating on airway remodeling in asthma, likely via a mechanism involving the suppression of TGF-β activation of RhoA.

Regulation of actin dynamics by WNT-5A: implications for human airway smooth muscle contraction

A defining feature of asthma is airway hyperresponsiveness (AHR), which underlies the exaggerated bronchoconstriction response of asthmatics. The role of the airway smooth muscle (ASM) in AHR has garnered increasing interest over the years, but how asthmatic ASM differs from healthy ASM is still an active topic of debate. WNT-5A is increasingly expressed in asthmatic ASM and has been linked with Th2-high asthma. Due to its link with calcium and cytoskeletal remodelling, we propose that WNT-5A may modulate ASM contractility. We demonstrated that WNT-5A can increase maximum isometric tension in bovine tracheal smooth muscle strips. In addition, we show that WNT-5A is preferentially expressed in contractile human airway myocytes compared to proliferative cells, suggesting an active role in maintaining contractility. Furthermore, WNT-5A treatment drives actin polymerisation, but has no effect on intracellular calcium flux. Next, we demonstrated that WNT-5A directly regulates TGF-β1-induced expression of α-SMA via ROCK-mediated actin polymerization. These findings suggest that WNT-5A modulates fundamental mechanisms that affect ASM contraction and thus may be of relevance for AHR in asthma.

Cooperative signaling by TGF-β1 and WNT-11 drives sm-α-actin expression in smooth muscle via Rho kinase-actin-MRTF-A signaling

Airway smooth muscle (ASM) remodeling is a key feature in asthma and includes changes in smooth muscle-specific gene and protein expression. Despite this being a major contributor to asthma pathobiology, our understanding of the mechanisms governing ASM remodeling remains poor. Here, we studied the functional interaction between WNT-11 and TGF-β1 in ASM cells. We demonstrate that WNT-11 is preferentially expressed in contractile myocytes and is strongly upregulated following TGF-β1-induced myocyte maturation. Knock-down of WNT-11 attenuated TGF-β1-induced smooth muscle (sm)-α-actin expression in ASM cells. We demonstrate that TGF-β1-induced sm-α-actin expression is mediated by WNT-11 via RhoA activation and subsequent actin cytoskeletal remodeling, as pharmacological inhibition of either Rho kinase by Y27632 or actin remodeling by latrunculin A attenuated sm-α-actin induction. Moreover, we show that TGF-β1 regulates the nuclear expression of myocardin-related transcription factor-A (MRTF-A) in a Rho kinase-dependent fashion, which in turn mediates sm-α-actin expression. Finally, we demonstrate that TGF-β1-induced MRTF-A nuclear translocation is dependent on endogenous WNT-11. The present study thus demonstrates a WNT-11-dependent Rho kinase-actin-MRTF-A signaling axis that regulates the expression of sm-α-actin in ASM cells.

Tumor necrosis factor regulates NMDA receptor-mediated airway smooth muscle contractile function and airway responsiveness

We have shown that N-methyl-d-aspartate receptors (NMDA-Rs) are receptor-operated calcium entry channels in human airway smooth muscle (HASM) during contraction. Tumor necrosis factor (TNF) augments smooth muscle contractility by influencing pathways that regulate intracellular calcium flux and can alter NMDA-R expression and activity in cortical neurons and glial cells. We hypothesized that NMDA-R-mediated Ca(2+) and contractile responses of ASM can be altered by inflammatory mediators, including TNF. In cultured HASM cells, we assessed TNF (10 ng/ml, 48 h) effect on NMDA-R subunit abundance by quantitative PCR, confocal imaging, and immunoblotting. We observed dose- and time-dependent changes in NMDA-R composition: increased obligatory NR1 subunit expression and altered regulatory NR2 and inhibitory NR3 subunits. Measuring intracellular Ca(2+) flux in Fura-2-loaded HASM cultures, we observed that TNF exposure enhanced cytosolic Ca(2+) mobilization and changed the temporal pattern of Ca(2+) flux in individual myocytes induced by NMDA, an NMDA-R selective analog of glutamate. We measured airway responses to NMDA in murine thin-cut lung slices (TCLS) from allergen-naive animals and observed significant airway contraction. However, NMDA acted as a bronchodilator in TCLS from house dust mice-challenged mice and in allergen-naive TCLS subjected to TNF exposure. All contractile or bronchodilator responses were blocked by a selective NMDA-R antagonist, (2R)-amino-5-phosphonopentanoate, and bronchodilator responses were prevented by N(G)-nitro-l-arginine methyl ester (nitric oxide synthase inhibitor) or indomethacin (cyclooxygenase inhibitor). Collectively, we show that TNF augments NMDA-R-mediated Ca(2+) mobilization in HASM cells, whereas in multicellular TCLSs allergic inflammation and TNF exposure leads to NMDA-R-mediated bronchodilation. These findings reveal the unique contribution of ionotrophic NMDA-R to airway hyperreactivity.

Caveolae - mechanosensitive membrane invaginations linked to actin filaments

An essential property of the plasma membrane of mammalian cells is its plasticity, which is required for sensing and transmitting of signals, and for accommodating the tensional changes imposed by its environment or its own biomechanics. Caveolae are unique invaginated membrane nanodomains that play a major role in organizing signaling, lipid homeostasis and adaptation to membrane tension. Caveolae are frequently associated with stress fibers, a major regulator of membrane tension and cell shape. In this Commentary, we discuss recent studies that have provided new insights into the function of caveolae and have shown that trafficking and organization of caveolae are tightly regulated by stress-fiber regulators, providing a functional link between caveolae and stress fibers. Furthermore, the tension in the plasma membrane determines the curvature of caveolae because they flatten at high tension and invaginate at low tension, thus providing a tension-buffering system. Caveolae also regulate multiple cellular pathways, including RhoA-driven actomyosin contractility and other mechanosensitive pathways, suggesting that caveolae could couple mechanotransduction pathways to actin-controlled changes in tension through their association with stress fibers. Therefore, we argue here that the association of caveolae with stress fibers could provide an important strategy for cells to deal with mechanical stress.

NMDA receptors mediate contractile responses in human airway smooth muscle cells

Human airway smooth muscle (HASM) exhibits enhanced contractility in asthma. Inflammation is associated with airway hypercontractility, but factors that underpin these features are not fully elucidated. Glutamate toxicity associated with increased plasma glutamate concentrations was observed in airway inflammation, suggesting that multisubunit glutamate receptors, N-methyl-d-aspartate receptors (NMDA-R) contribute to airway hyperreactivity. We tested the hypothesis that HASM expresses NMDA-R subunits that can form functional receptors to mediate contractile responses to specific extracellular ligands. In cultured HASM cells, we measured NMDA-R subunit mRNA and protein abundance by quantitative PCR, immunoblotting, flow cytometry, and epifluorescence immunocytochemistry. We measured mRNA for a number of NMDA-R subunits, including the obligatory NR1 subunit, which we confirmed to be present as a protein. In vitro and ex vivo functional NMDA-R activation in HASM cells was measured using intracellular calcium flux (fura-2 AM), collagen gel contraction assays, and murine thin-cut lung slices (TCLS). NMDA, a pharmacological glutamate analog, induced cytosolic calcium mobilization in cultured HASM cells. We detected three different temporal patterns of calcium response, suggesting the presence of heterogeneous myocyte subpopulations. NMDA-R activation also induced airway contraction in murine TCLS and soft collagen gels seeded with HASM cells. Responses in cells, lung slices, and collagen gels were mediated by NMDA-R, as they could be blocked by (2R)-amino-5-phosphonopentanoate, a specific NMDA-R inhibitor. In summary, we reveal the presence of NMDA-R in HASM that mediate contractile responses via glutamatergic mechanisms. These findings suggest that accumulation of glutamate-like ligands for NMDA-R associated with airway inflammation contributes directly to airway hyperreactivity.

Antigen-induced airway hyperresponsiveness and obstruction is related to caveolin-1 expression in airway smooth muscle in a guinea pig asthma model

BACKGROUND

Caveolin-1 is a fundamental signalling scaffold protein involved in contraction; however, the role of caveolin-1 in airway responsiveness remains unclear. We evaluated the relationship between caveolin-1 expression in airway smooth muscle (ASM) and antigen-induced airway responsiveness and obstruction in a guinea pig asthma model.

METHODS

Airway obstruction in sensitised guinea pigs, induced by antigenic (ovalbumin) challenges administered every 10 days, was measured. Antigen-induced responsiveness to histamine and the expression of caveolin-1 and cavin 1, 2 and 3 were evaluated at the third ovalbumin challenge. The control group received saline solution instead of ovalbumin.

RESULTS

After the first challenge, antigen exposure induced a transient airway obstruction and airway hyperresponsiveness, high levels of IL-4 and IL-5 in lung and airway globet cells proliferation at the third antigenic challenge. Caveolin-1 mRNA levels in total lung decreased in the experimental group compared with controls. Flow cytometric analysis of ASM from the experimental group showed a high number of cells expressing caveolin-1 compared with controls. This increase was confirmed by western blot. Airway obstruction and hyperresponsiveness correlated with the degree of increased caveolin-1 expression in ASM cells (P < 0.05; r = 0.69 and -0.52, respectively). The expression of cavins 1, 2 and 3 in ASM also increased in the experimental group compared to controls. Immunohistochemical findings reveal that differences in ASM caveolin-1 were not evident between groups. Nevertheless, a marked decrease in caveolin-1 and caspase 3 was observed in the pulmonary vascular smooth muscle of asthma model compared with controls. Histological analysis did not reveal differences in smooth muscles mass or subepithelial fibrosis levels in airways between groups. However, an enlargement of smooth muscle mass was observed in the pulmonary microvessels of experimental animals. This enlargement did not induce changes in pulmonary or systemic arterial pressures.

CONCLUSIONS

Our data suggest that caveolin-1 expression in ASM has a crucial role in the development of antigen-induced airway obstruction and hyperresponsiveness in a guinea pig asthma model. In addition, the asthma model in guinea pigs appears to induce a contractile smooth muscle phenotype in the airways and a proliferative smooth muscle phenotype in pulmonary vessels.

Role of dystrophin in airway smooth muscle phenotype, contraction and lung function

Dystrophin links the transmembrane dystrophin-glycoprotein complex to the actin cytoskeleton. We have shown that dystrophin-glycoprotein complex subunits are markers for airway smooth muscle phenotype maturation and together with caveolin-1, play an important role in calcium homeostasis. We tested if dystrophin affects phenotype maturation, tracheal contraction and lung physiology. We used dystrophin deficient Golden Retriever dogs (GRMD) and mdx mice vs healthy control animals in our approach. We found significant reduction of contractile protein markers: smooth muscle myosin heavy chain (smMHC) and calponin and reduced Ca2+ response to contractile agonist in dystrophin deficient cells. Immunocytochemistry revealed reduced stress fibers and number of smMHC positive cells in dystrophin-deficient cells, when compared to control. Immunoblot analysis of Akt1, GSK3β and mTOR phosphorylation further revealed that downstream PI3K signaling, which is essential for phenotype maturation, was suppressed in dystrophin deficient cell cultures. Tracheal rings from mdx mice showed significant reduction in the isometric contraction to methacholine (MCh) when compared to genetic control BL10ScSnJ mice (wild-type). In vivo lung function studies using a small animal ventilator revealed a significant reduction in peak airway resistance induced by maximum concentrations of inhaled MCh in mdx mice, while there was no change in other lung function parameters. These data show that the lack of dystrophin is associated with a concomitant suppression of ASM cell phenotype maturation in vitro, ASM contraction ex vivo and lung function in vivo, indicating that a linkage between the DGC and the actin cytoskeleton via dystrophin is a determinant of the phenotype and functional properties of ASM.

Role of caveolin-1 in asthma and chronic inflammatory respiratory diseases

Caveolin-1 (Cav-1) is the major protein present in invaginations of the plasma membrane of cells known as caveolae. Cav-1 is expressed in numerous resident and inflammatory cells implicated in the pathogenesis of asthma and chronic inflammatory respiratory diseases including chronic obstructive pulmonary disease. A remarkable repertoire of functions has been identified for Cav-1 and these extend to, and have relevance to, asthma and chronic inflammatory respiratory diseases. Important processes influenced by Cav-1 include inflammation, fibrosis, smooth muscle contractility, regulation of apoptosis and cell senescence as well as epithelial barrier function and homeostasis. A better understanding of Cav-1 may be useful in developing new therapies for chronic inflammatory respiratory diseases.

The role of caveolae in the pathophysiology of lung diseases

Caveolae are flask-shaped plasma membrane invaginations formed by constitutive caveolin proteins and regulatory cavin proteins. Caveolae harbor a range of signaling components such as receptors, ion channels and regulatory molecules. There is now increasing evidence that caveolins and cavins play an important role in a variety of diseases. However, the mechanisms by which these caveolar proteins affect lung health and disease are still under investigation, with emerging data suggesting complex roles in disease pathophysiology. This review summarizes the current state of understanding of how caveolar proteins contribute to lung structure and function and how their altered expression and/or function can influence lung diseases.

Airway smooth muscle in airway reactivity and remodeling: what have we learned?

It is now established that airway smooth muscle (ASM) has roles in determining airway structure and function, well beyond that as the major contractile element. Indeed, changes in ASM function are central to the manifestation of allergic, inflammatory, and fibrotic airway diseases in both children and adults, as well as to airway responses to local and environmental exposures. Emerging evidence points to novel signaling mechanisms within ASM cells of different species that serve to control diverse features, including 1) [Ca(2+)]i contractility and relaxation, 2) cell proliferation and apoptosis, 3) production and modulation of extracellular components, and 4) release of pro- vs. anti-inflammatory mediators and factors that regulate immunity as well as the function of other airway cell types, such as epithelium, fibroblasts, and nerves. These diverse effects of ASM "activity" result in modulation of bronchoconstriction vs. bronchodilation relevant to airway hyperresponsiveness, airway thickening, and fibrosis that influence compliance. This perspective highlights recent discoveries that reveal the central role of ASM in this regard and helps set the stage for future research toward understanding the pathways regulating ASM and, in turn, the influence of ASM on airway structure and function. Such exploration is key to development of novel therapeutic strategies that influence the pathophysiology of diseases such as asthma, chronic obstructive pulmonary disease, and pulmonary fibrosis.

Airway hyperresponsiveness is associated with airway remodeling but not inflammation in aging Cav1-/- mice

Background

Airway inflammation and airway remodeling are the key contributors to airway hyperresponsiveness (AHR), a characteristic feature of asthma. Both processes are regulated by Transforming Growth Factor (TGF)-β. Caveolin 1 (Cav1) is a membrane bound protein that binds to a variety of receptor and signaling proteins, including the TGF-β receptors. We hypothesized that caveolin-1 deficiency promotes structural alterations of the airways that develop with age will predispose to an increased response to allergen challenge.

Methods

AHR was measured in Cav1-deficient and wild-type (WT) mice 1 to 12 months of age to examine the role of Cav1 in AHR and the relative contribution of inflammation and airway remodeling. AHR was then measured in Cav1^-/- and WT mice after an ovalbumin-allergen challenge performed at either 2 months of age, when remodeling in Cav1^-/- and WT mice was equivalent, and at 6 months of age, when the Cav1^-/- mice had established airway remodeling.

Results

Cav1^-/- mice developed increased thickness of the subepithelial layer and a correspondingly increased AHR as they aged. In addition, allergen-challenged Cav1^-/- mice had an increase in AHR greater than WT mice that was largely independent of inflammation. Cav1^-/- mice challenged at 6 months of age have decreased AHR compared to those challenged at 2 months with correspondingly decreased BAL IL-4 and IL-5 levels, inflammatory cell counts and percentage of eosinophils. In addition, in response to OVA challenge, the number of goblet cells and α-SMA positive cells in the airways were reduced with age in response to OVA challenge in contrast to an increased collagen deposition further enhanced in absence of Cav1.

Conclusion

A lack of Cav1 contributed to the thickness of the subepithelial layer in mice as they aged resulting in an increase in AHR independent of inflammation, demonstrating the important contribution of airway structural changes to AHR. In addition, age in the Cav1^-/- mice is a contributing factor to airway remodeling in the response to allergen challenge.

Lovastatin-induced decrease of intracellular cholesterol level attenuates fibroblast-to-myofibroblast transition in bronchial fibroblasts derived from asthmatic patients

Chronic inflammation of the airways and structural changes in the bronchial wall are basic hallmarks of asthma. Human bronchial fibroblasts derived from patients with diagnosed asthma display in vitro predestination towards TGF-β-induced fibroblast-to-myofibroblast transition (FMT), a key event in the bronchial wall remodelling. Statins inhibit 3-hydroxymethyl-3-glutaryl coenzyme A reductase, a key enzyme in the cholesterol synthesis pathway and are widely used as antilipidemic drugs. The pleiotropic anti-inflammatory effects of statins, independent of their cholesterol-lowering capacity, are also well established. Since commonly used anti-asthmatic drugs do not reverse the structural remodelling of the airways and statins have tentative anti-asthmatic activity, we have studied the effect of lovastatin on FMT in populations of human bronchial fibroblasts derived from asthmatic patients. We demonstrate that the intensity of FMT induced by TGF-β1 was strongly and dose-dependently attenuated by lovastatin. Furthermore, we show that neither the suppression of prenylation of signalling proteins nor the effect on reactive oxygen species formation are important for lovastatin-induced inhibition of myofibroblast differentiation. On the other hand, we show that a squalene synthase inhibitor, zaragozic acid A, reduced the TGF-β1-induced FMT to an extent comparable to lovastatin effect. Additionally we demonstrate that in bronchial fibroblast populations, both inhibitors (lovastatin and zaragozic acid A) attenuate the TGF-β1-induced Smad2 nuclear translocation in a manner dependent on intracellular cholesterol level. Our data suggest that statins can directly, by decrease of intracellular cholesterol level, affect basic cell signalling events crucial for asthmatic processes and potentially prevent perilous bronchial wall remodelling associated with intensive myofibroblast formation.

Antenatal glucocorticoids counteract LPS changes in TGF-β pathway and caveolin-1 in ovine fetal lung

Inflammation and antenatal glucocorticoids, the latter given to mothers at risk for preterm birth, affect lung development and may contribute to the development of bronchopulmonary dysplasia (BPD). The effects of the combined exposures on inflammation and antenatal glucocorticoids on transforming growth factor (TGF)-β signaling are unknown. TGF-β and its downstream mediators are implicated in the etiology of BPD. Therefore, we asked whether glucocorticoids altered intra-amniotic lipopolysaccharide (LPS) effects on TGF-β expression, its signaling molecule phosphorylated sma and mothers against decapentaplegic homolog 2 (pSmad2), and the downstream mediators connective tissue growth factor (CTGF) and caveolin-1 (Cav-1). Ovine singleton fetuses were randomized to receive either an intra-amniotic injection of LPS and/or maternal betamethasone (BTM) intramuscularly 7 and/or 14 days before delivery at 120 days gestational age (GA; term = 150 days GA). Saline was used for controls. Protein levels of TGF-β1 and -β2 were measured by ELISA. Smad2 phosphorylation was assessed by immunohistochemistry and Western blot. CTGF and Cav-1 mRNA and protein levels were determined by RT-PCR and Western blot. Free TGF-β1 and -β2 and total TGF-β1 levels were unchanged after LPS and/or BTM exposure, although total TGF-β2 increased in animals exposed to BTM 7 days before LPS. pSmad2 immunostaining increased 7 days after LPS exposure although pSmad2 protein expression did not increase. Similarly, CTGF mRNA and protein levels increased 7 days after LPS exposure as Cav-1 mRNA and protein levels decreased. BTM exposure before LPS prevented CTGF induction and Cav-1 downregulation. This study demonstrated that the intrauterine inflammation-induced TGF-β signaling can be inhibited by antenatal glucocorticoids in fetal lungs.

Epithelium-dependent modulation of responsiveness of airways from caveolin-1 knockout mice is mediated through cyclooxygenase-2 and 5-lipoxygenase

BACKGROUND AND PURPOSE

Acute silencing of caveolin-1 (Cav-1) modulates receptor-mediated contraction of airway smooth muscle. Moreover, COX-2- and 5-lipoxygenase (5-LO)-derived prostaglandin and leukotriene biosynthesis can influence smooth muscle reactivity. COX-2 half-life can be prolonged through association with Cav-1. We suggested that lack of Cav-1 modulated levels of COX-2 which in turn modulated tracheal contraction, when arachidonic acid signalling was disturbed by inhibition of COX-2.

EXPERIMENTAL APPROACH

Using tracheal rings from Cav-1 knockout (KO) and wild-type mice (B6129SF2/J), we measured isometric contractions to methacholine and used PCR, immunoblotting and immunohistology to monitor expression of relevant proteins.

KEY RESULTS

Tracheal rings from Cav-1 KO and wild-type mice exhibited similar responses, but the COX-2 inhibitor, indomethacin, increased responses of tracheal rings from Cav-1 KO mice to methacholine. The phospholipase A₂ inhibitor, eicosatetraynoic acid, which inhibits formation of both COX-2 and 5-LO metabolites, had no effect on wild-type or Cav-1 KO tissues. Indomethacin-mediated hyperreactivity was ablated by the LTD₄ receptor antagonist (montelukast) and 5-LO inhibitor (zileuton). The potentiating effect of indomethacin on Cav-1 KO responses to methacholine was blocked by epithelial denudation. Immunoprecipitation showed that COX-2 binds Cav-1 in wild-type lungs. Immunoblotting and qPCR revealed elevated levels of COX-2 and 5-LO protein, but not COX-1, in Cav-1 KO tracheas, a feature that was prevented by removal of the epithelium.

CONCLUSION AND IMPLICATIONS

The indomethacin-induced hypercontractility observed in Cav-1 KO tracheas was linked to increased expression of COX-2 and 5-LO, which probably enhanced arachidonic acid shunting and generation of pro-contractile leukotrienes when COX-2 was inhibited.

Distinct PKA and Epac compartmentalization in airway function and plasticity

Asthma and chronic obstructive pulmonary disease (COPD) are obstructive lung diseases characterized by airway obstruction, airway inflammation and airway remodelling. Next to inflammatory cells and airway epithelial cells, airway mesenchymal cells, including airway smooth muscle cells and (myo)fibroblasts, substantially contribute to disease features by the release of inflammatory mediators, smooth muscle contraction, extracellular matrix deposition and structural changes in the airways. Current pharmacological treatment of both diseases intends to target the dynamic features of the endogenous intracellular suppressor cyclic AMP (cAMP). This review will summarize our current knowledge on cAMP and will emphasize on key discoveries and paradigm shifts reflecting the complex spatio-temporal nature of compartmentalized cAMP signalling networks in health and disease. As airway fibroblasts and airway smooth muscle cells are recognized as central players in the development and progression of asthma and COPD, we will focus on the role of cAMP signalling in their function in relation to airway function and plasticity. We will recapture on the recent identification of cAMP-sensing multi-protein complexes maintained by cAMP effectors, including A-kinase anchoring proteins (AKAPs), proteins kinase A (PKA), exchange protein directly activated by cAMP (Epac), cAMP-elevating seven-transmembrane (7TM) receptors and phosphodiesterases (PDEs) and we will report on findings indicating that the pertubation of compartmentalized cAMP signalling correlates with the pathopysiology of obstructive lung diseases. Future challenges include studies on cAMP dynamics and compartmentalization in the lung and the development of novel drugs targeting these systems for therapeutic interventions in chronic obstructive inflammatory diseases.

Muscarinic receptor stimulation augments TGF-β1-induced contractile protein expression by airway smooth muscle cells

Acetylcholine (ACh) is the primary parasympathetic neurotransmitter in the airways. Recently, it was established that ACh, via muscarinic receptors, regulates airway remodeling in animal models of asthma and chronic obstructive pulmonary disease (COPD). The mechanisms involved are not well understood. Here, we investigated the functional interaction between muscarinic receptor stimulation and transforming growth factor (TGF)-β(1) on the expression of contractile proteins in human airway smooth muscle (ASM) cells. ASM cells expressing functional muscarinic M(2) and M(3) receptors were stimulated with methacholine (MCh), TGF-β(1), or their combination for up to 7 days. Western blot analysis revealed a strong induction of sm-α-actin and calponin by TGF-β(1), which was increased by MCh in ASM cells. Immunocytochemistry confirmed these results and revealed that the presence of MCh augmented the formation of sm-α-actin stress fibers by TGF-β(1). MCh did not augment TGF-β(1)-induced gene transcription of contractile phenotype markers. Rather, translational processes were involved in the augmentation of TGF-β(1)-induced contractile protein expression by muscarinic receptor stimulation, including phosphorylation of glycogen synthase kinase-3β and 4E-binding protein 1, which was enhanced by MCh. In conclusion, muscarinic receptor stimulation augments functional effects of TGF-β(1) in human ASM cells on cellular processes that underpin ASM remodeling in asthma and COPD.

Muscarinic receptors on airway mesenchymal cells: novel findings for an ancient target

Since ancient times, anticholinergics have been used as a bronchodilator therapy for obstructive lung diseases. Targets of these drugs are G-protein-coupled muscarinic M(1), M(2) and M(3) receptors in the airways, which have long been recognized to regulate vagally-induced airway smooth muscle contraction and mucus secretion. However, recent studies have revealed that acetylcholine also exerts pro-inflammatory, pro-proliferative and pro-fibrotic actions in the airways, which may involve muscarinic receptor stimulation on mesenchymal, epithelial and inflammatory cells. Moreover, acetylcholine in the airways may not only be derived from vagal nerves, but also from non-neuronal cells, including epithelial and inflammatory cells. Airway smooth muscle cells seem to play a major role in the effects of acetylcholine on airway function. It has become apparent that these cells are multipotent cells that may reversibly adopt (hyper)contractile, proliferative and synthetic phenotypes, which are all under control of muscarinic receptors and differentially involved in bronchoconstriction, airway remodeling and inflammation. Cholinergic contractile tone is increased by airway inflammation associated with asthma and COPD, resulting from exaggerated acetylcholine release as well as increased expression of contraction related proteins in airway smooth muscle. Moreover, muscarinic receptor stimulation promotes proliferation of airway smooth muscle cells as well as fibroblasts, and regulates cytokine, chemokine and extracellular matrix production by these cells, which may contribute to airway smooth muscle growth, airway fibrosis and inflammation. In line, animal models of chronic allergic asthma and COPD have recently demonstrated that tiotropium may potently inhibit airway inflammation and remodeling. These observations indicate that muscarinic receptors have a much larger role in the pathophysiology of obstructive airway diseases than previously thought, which may have important therapeutic implications.

Stimulus-specific activation and actin dependency of distinct, spatially separated ERK1/2 fractions in A7r5 smooth muscle cells

A proliferative response of smooth muscle cells to activation of extracellular signal regulated kinases 1 and 2 (ERK1/2) has been linked to cardiovascular disease. In fully differentiated smooth muscle, however, ERK1/2 activation can also regulate contraction. Here, we use A7r5 smooth muscle cells, stimulated with 12-deoxyphorbol 13-isobutylate 20-acetate (DPBA) to induce cytoskeletal remodeling or fetal calf serum (FCS) to induce proliferation, to identify factors that determine the outcomes of ERK1/2 activation in smooth muscle. Knock down experiments, immunoprecipitation and proximity ligation assays show that the ERK1/2 scaffold caveolin-1 mediates ERK1/2 activation in response to DPBA, but not FCS, and that ERK1/2 is released from caveolin-1 upon DPBA, but not FCS, stimulation. Conversely, ERK1/2 associated with the actin cytoskeleton is significantly reduced after FCS, but not DPBA stimulation, as determined by Triton X fractionation. Furthermore, cytochalasin treatment inhibits DPBA, but not FCS-induced ERK1/2 phosphorylation, indicating that the actin cytoskeleton is not only a target but also is required for ERK1/2 activation. Our results show that (1) at least two ERK1/2 fractions are regulated separately by specific stimuli, and that (2) the association of ERK1/2 with the actin cytoskeleton regulates the outcome of ERK1/2 signaling.

Laser scanning cytometry: principles and applications-an update

Laser scanning cytometer (LSC) is the microscope-based cytofluorometer that offers a plethora of unique analytical capabilities, not provided by flow cytometry (FCM). This review describes attributes of LSC and covers its numerous applications derived from plentitude of the parameters that can be measured. Among many LSC applications the following are emphasized: (a) assessment of chromatin condensation to identify mitotic, apoptotic cells, or senescent cells; (b) detection of nuclear or mitochondrial translocation of critical factors such as NF-κB, p53, or Bax; (c) semi-automatic scoring of micronuclei in mutagenicity assays; (d) analysis of fluorescence in situ hybridization (FISH) and use of the FISH analysis attribute to measure other punctuate fluorescence patterns such as γH2AX foci or receptor clustering; (e) enumeration and morphometry of nucleoli and other cell organelles; (f) analysis of progeny of individual cells in clonogenicity assay; (g) cell immunophenotyping; (h) imaging, visual examination, or sequential analysis using different probes of the same cells upon their relocation; (i) in situ enzyme kinetics, drug uptake, and other time-resolved processes; (j) analysis of tissue section architecture using fluorescent and chromogenic probes; (k) application for hypocellular samples (needle aspirate, spinal fluid, etc.); and (l) other clinical applications. Advantages and limitations of LSC are discussed and compared with FCM.

Caveolin-1 in cytokine-induced enhancement of intracellular Ca(2+) in human airway smooth muscle

Diseases such as asthma are characterized by airway hyperresponsiveness. Enhanced airway smooth muscle (ASM) intracellular Ca(2+) ([Ca(2+)](i)) response to agonist stimulation leading to increased airway constriction has been suggested to contribute to airway hyperresponsiveness. Caveolae are flask-shaped plasma membrane invaginations that express the scaffolding protein caveolin and contain multiple proteins important in [Ca(2+)](i) signaling (e.g., agonist receptors, ion channels). We recently demonstrated that caveolae and caveolin-1 are important in [Ca(2+)](i) regulation in human ASM. Proinflammatory cytokines such as tumor necrosis factor (TNF)-α and interleukin (IL)-13 modulate [Ca(2+)](i) in ASM. We hypothesized that cytokine upregulation of caveolar signaling in ASM contributes to enhanced agonist-induced [Ca(2+)](i) in inflammation. Enzymatically dissociated human ASM cells were exposed to medium (control), 20 ng/ml TNF-α, or 50 ng/ml IL-13 for 24 h. Caveolae-enriched membrane fractions displayed substantial increase in caveolin-1 and -2 expressions by TNF-α and IL-13. Transfection with caveolin-1-mRed DNA substantially accelerated and increased plasma membrane caveolin-1 expression by TNF-α and to a lesser extent by IL-13. Caveolin-1 enhancement was inhibited by nuclear factor-κB and mitogen-activated protein kinase inhibitors. In fura 2-loaded ASM cells, [Ca(2+)](i) responses to 1 μM ACh, 10 μM histamine, or 10 nM bradykinin were all exaggerated by TNF-α as well as IL-13 exposure. However, disruption of caveolae using caveolin-1 suppression via small-interfering RNA resulted in significant blunting of agonist-induced [Ca(2+)](i) responses of vehicle and TNF-α-exposed cells. These functional data were correlated to the presence of TNFR(1) receptor (but not the IL-4/IL-13 receptor) within caveolae. Overall, these results indicate that caveolin-1 plays an important role in airway inflammation by modulating the effect of specific cytokines on [Ca(2+)](i).

Cell-specific dual role of caveolin-1 in pulmonary hypertension

A wide variety of cardiopulmonary and systemic diseases are known to lead to pulmonary hypertension (PH). A number of signaling pathways have been implicated in PH; however, the precise mechanism/s leading to PH is not yet clearly understood. Caveolin-1, a membrane scaffolding protein found in a number of cells including endothelial and smooth muscle cells, has been implicated in PH. Loss of endothelial caveolin-1 is reported in clinical and experimental forms of PH. Caveolin-1, also known as a tumor-suppressor factor, interacts with a number of transducing molecules that reside in or are recruited to caveolae, and it inhibits cell proliferative pathways. Not surprisingly, the rescue of endothelial caveolin-1 has been found not only to inhibit the activation of proliferative pathways but also to attenuate PH. Recently, it has emerged that during the progression of PH, enhanced expression of caveolin-1 occurs in smooth muscle cells, where it facilitates cell proliferation, thus contributing to worsening of the disease. This paper summarizes the cell-specific dual role of caveolin-1 in PH.

Caveolin-1 and force regulation in porcine airway smooth muscle

Caveolae are specialized membrane microdomains expressing the scaffolding protein caveolin-1. We recently demonstrated the presence of caveolae in human airway smooth muscle (ASM) and the contribution of caveolin-1 to intracellular calcium ([Ca(2+)](i)) regulation. In the present study, we tested the hypothesis that caveolin-1 regulates ASM contractility. We examined the role of caveolins in force regulation of porcine ASM under control conditions as well as TNF-α-induced airway inflammation. In porcine ASM strips, exposure to 10 mM methyl-β-cyclodextrin (CD) or 5 μM of the caveolin-1 specific scaffolding domain inhibitor peptide (CSD) resulted in time-dependent decrease in force responses to 1 μM ACh. Overnight exposure to the cytokine TNF-α (50 ng/ml) accelerated and increased caveolin-1 expression and enhanced force responses to ACh. Suppression of caveolin-1 with small interfering RNA mimicked the effects of CD or CSD. Regarding mechanisms by which caveolae contribute to contractile changes, inhibition of MAP kinase with 10 μM PD98059 did not alter control or TNF-α-induced increases in force responses to ACh. However, inhibiting RhoA with 100 μM fasudil or 10 μM Y27632 resulted in significant decreases in force responses, with lesser effects in TNF-α exposed samples. Furthermore, Ca(2+) sensitivity for force generation was substantially reduced by fasudil or Y27632, an effect even more enhanced in the absence of caveolin-1 signaling. Overall, these results indicate that caveolin-1 is a critical player in enhanced ASM contractility with airway inflammation.